#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <climits>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <stack>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <sstream>
#include <functional>
#include <ctime>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> PII;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n)  FOR(i,0,n)
#define CLEAR(d) memset((d), 0, (sizeof((d))))
#define ALL(c) (c).begin(), (c).end()
#define ABS(x) ((x < 0) ? -(x) : (x))
#define SORT(x) sort((x).begin(), (x).end())
#define RSORT(x) sort((x).begin(), (x).end(), greater<int>() )
#define SIZE(a) ((int)((a).size()))
#define MOD 1000000007
#define EPS 1e-10
#define PI  (acos(-1))
#define INF 10000000
struct edge { int to; int cost; };
//===================================================

int main()
{
    int n, m, k, a, b, c;
    vector<edge> e[1001];
    cin >> n >> m >> k;
    vector<int> d(k);
    REP(i, m) {
        cin >> a >> b >> c;
        edge e1 = { a, c }, e2 = { b, c };
        e[b].push_back(e1);
        e[a].push_back(e2);
    }
    int node[101] = {};
    stack<int> s;
    for (int i = 0; i < k; i++) {
        cin >> d[i];
        if (i == 0) {
            for (int j = 1; j <= n; j++) {
                for (int k = 0; k < e[j].size(); k++) {
                    if (e[j][k].cost == d[i]) {
                        node[e[j][k].to] = 1;
                        //node[j] = 1;
                    }
                }
            }
            for (int j = 1; j <= n; j++) {
                if (node[j] == 1) s.push(j);
            }
        }
        else {
            CLEAR(node);
            while (!s.empty()) {
                int t = s.top(); s.pop();
                for (int j = 0; j < e[t].size(); j++) {
                    if (e[t][j].cost == d[i]) node[e[t][j].to] = 1;
                }
            }
            for (int j = 1; j <= n; j++) {
                if (node[j] == 1) {
                    s.push(j);

                }
            }
        }
    }
    vector<int> ans;
    while (!s.empty()) {
        ans.push_back(s.top());
        s.pop();
    }
    int sz = ans.size();
    cout << sz << endl;
    SORT(ans);
    for (int i = 0; i < sz; i++) {
        printf("%d", ans[i]);
        if (i < sz - 1) printf(" ");
    }
    puts("");
    return 0;
}